One reason I am willing to pay Safari IT ~ 500 per year for
an unlimited library shelf of technical e-books is that most of the time I don't need either the absolute latest edition or a book on a specialized aspect of IT; when I do, I expect to pay for it.
However, just like books they have on the
shelves,
libraries have the right to lend your audiobook an
unlimited number of times as long as they are only giving one patron access at a time.